operator function 是什么

在编程中，"operator function" 通常是指操作符重载（Operator Overloading），这是允许程序员自定义已经存在的运算符，使其在特定类型的上下文中有特殊含义的行为。这种技术常见于支持类和对象的语言，例如C++、C#和Java。

例如，在C++中，你可以创建一个类，并通过重载 '+' 运算符，使得当你对这个类的对象进行加法操作时，实际上会调用你自定义的方法，而不仅仅是普通的数值相加。例如：

class Complex {
public:
    Complex(double real, double imag) : real_(real), imag_(imag) {}
    Complex& operator+(const Complex& other) { /* 自定义的加法计算 */ }
private:
    double real_;
    double imag_;
};

Complex c1(1, 2);
Complex c2(3, 4);
Complex result = c1 + c2;  // 实际上调用了我们自定义的加法运算

在这样的场景下，`operator+`就是一个操作符函数，它改变了原始运算符的行为，使其适应特定的数据结构。

相关问题

write an overloaded friend ostream insertion operator function that allows a Fraction object to be output and appear in the form num/denom, using a cout statement. b. Write an overloaded friend istream extraction operator function that allows fractions in the form a/b to be input and assigned to a Fraction object.

Sure, I can help you with that!

Here is the implementation of the overloaded friend ostream insertion operator function for the Fraction class:

#include <iostream>

class Fraction {
    private:
        int numerator;
        int denominator;
    public:
        Fraction(int num, int denom) : numerator(num), denominator(denom) { }
        friend std::ostream& operator<<(std::ostream& os, const Fraction& frac);
};

std::ostream& operator<<(std::ostream& os, const Fraction& frac) {
    os << frac.numerator << "/" << frac.denominator;
    return os;
}

And here is the implementation of the overloaded friend istream extraction operator function for the Fraction class:

#include <iostream>
#include <sstream>

class Fraction {
    private:
        int numerator;
        int denominator;
    public:
        Fraction(int num, int denom) : numerator(num), denominator(denom) { }
        friend std::istream& operator>>(std::istream& is, Fraction& frac);
};

std::istream& operator>>(std::istream& is, Fraction& frac) {
    std::string input;
    is >> input;
    std::stringstream ss(input);
    int num, denom;
    char slash;
    ss >> num >> slash >> denom;
    frac.numerator = num;
    frac.denominator = denom;
    return is;
}

You can use these overloaded operators to output and input Fraction objects as follows:

int main() {
    Fraction f1(3, 4);
    std::cout << f1 << std::endl; // outputs "3/4"
    
    Fraction f2(0, 1);
    std::cin >> f2; // inputs a Fraction from standard input in the form "num/denom"
    std::cout << f2 << std::endl; // outputs the input Fraction
    
    return 0;
}

I hope this helps! Let me know if you have any other questions.

Write a simple function template for predict function isEqualTo that compares its two arguments of the same type with the equality operator (==) and returns true if they are equal and false if they are not equal. Use this function template in a program that calls isEqualTo only with a variety of built-in types. Now write a separate version of the program that calls isEqualTo with a user-defined class type Complex, but does not overload the equality operator. What happens when you attempt to run this program? Now overload the equality operator (with the operator function) operator ==. Now what happens when you attempt to run this program?

Here is the function template for isEqualTo:

template<typename T>
bool isEqualTo(const T& a, const T& b) {
    return a == b;
}

Here is an example program that uses isEqualTo with built-in types:

#include <iostream>

int main() {
    std::cout << std::boolalpha;
    std::cout << isEqualTo(5, 5) << std::endl;
    std::cout << isEqualTo(5, 7) << std::endl;
    std::cout << isEqualTo('a', 'a') << std::endl;
    std::cout << isEqualTo('a', 'b') << std::endl;
    std::cout << isEqualTo(true, true) << std::endl;
    std::cout << isEqualTo(true, false) << std::endl;
    std::cout << isEqualTo(3.14, 3.14) << std::endl;
    std::cout << isEqualTo(3.14, 2.71) << std::endl;
    return 0;
}

When we attempt to run this program with the user-defined class type Complex, we get a compilation error because the compiler doesn't know how to compare two Complex objects.

To fix this, we can overload the equality operator in the Complex class:

class Complex {
public:
    Complex(double real, double imag) : m_real(real), m_imag(imag) {}
    double real() const { return m_real; }
    double imag() const { return m_imag; }
private:
    double m_real;
    double m_imag;
};

bool operator==(const Complex& lhs, const Complex& rhs) {
    return lhs.real() == rhs.real() && lhs.imag() == rhs.imag();
}

Now when we attempt to run the program with Complex objects, it works as expected:

#include <iostream>

class Complex {
public:
    Complex(double real, double imag) : m_real(real), m_imag(imag) {}
    double real() const { return m_real; }
    double imag() const { return m_imag; }
private:
    double m_real;
    double m_imag;
};

bool operator==(const Complex& lhs, const Complex& rhs) {
    return lhs.real() == rhs.real() && lhs.imag() == rhs.imag();
}

template<typename T>
bool isEqualTo(const T& a, const T& b) {
    return a == b;
}

int main() {
    std::cout << std::boolalpha;
    std::cout << isEqualTo(Complex(1.0, 2.0), Complex(1.0, 2.0)) << std::endl;
    std::cout << isEqualTo(Complex(1.0, 2.0), Complex(3.0, 4.0)) << std::endl;
    return 0;
}

Output:

true
false